Process and an apparatus for producing metals and metal alloys

ABSTRACT

A process and an apparatus for producing metals from a metalliferous feed material are disclosed. The process includes the steps of partially reducing and at least partially melting a metalliferous feed material in a pre-reduction/melting means and completely reducing the partially reduced feed material in a reduction means. The pre-reduction/melting means is positioned directly above the reduction means and communicates with the reduction means so that at least partially molten, partially reduced feed material flows downwardly into a central region of the reduction means. The reduction means includes a vessel that contains a molten bath having a metal layer and a slag layer on the metal layer. The process includes injecting oxygen-containing gas into the reduction means and post-combusting reaction gas generated in the molten bath and injecting oxygen-containing gas into the pre-reduction/melting means and post-combusting reaction gas discharged from the reduction means. The process further includes injecting solid carbonaceous material and a carrier gas into a metal rich region of the molten bath and causing upward movement of splashes, droplets and streams of molten material which forms a transition zone.

The present invention relates to a process for producing molten metal(which term includes metal alloys), in particular, although by no meansexclusively iron, from a metalliferous feed material, such as ores,partly reduced ores and metal-containing waste streams, in ametallurgical vessel containing a molten bath.

The present invention relates particularly to a process and an apparatusfor producing molten metal from a metalliferous feed material which isbased on the combination of:

(a) a means which partially reduces and at least partially melts themetalliferous feed material; and

(b) a means which completes reduction of the molten partially-reducedfeed material.

One example of a pre-reduction/melting means is a cyclone converter.

One example of a reduction means is a vessel that contains a moltenbath.

U.S. Pat. No. 4,849,015 of Fassbinder et al and U.S. Pat. No. 5,800,592of Den Hartog et al disclose particular proposals for producing molteniron from iron ore using the above combination of pre-reduction/meltingmeans and reduction means.

One object of the present invention is to provide an alternativeprocess/apparatus for producing molten iron from iron ore which is basedon the above combination of pre-reduction/melting means and reductionmeans.

According to the present invention there is provided a process forproducing metals from a metalliferous feed material which includes thesteps of partially reducing and at least partially melting themetalliferous feed material in a pre-reduction/melting means andcompletely reducing the partially reduced feed material in a reductionmeans, which reduction means includes a vessel that contains a moltenbath having a metal layer and a slag layer on the metal layer, and whichprocess is characterised by:

(a) injecting solid carbonaceous material with a carrier gas into ametal rich region of the molten bath;

(b) causing upward movement of splashes, droplets, and streams ofmaterial from the metal layer which:

(i) promotes mixing of material from the metal layer in the slag layerand mixing of material from the slag layer in the metal layer; and

(ii) extends into a space above the molten bath to form a transitionzone;

(c) injecting an oxygen-containing gas into the vessel andpost-combusting part of a reaction gas generated in the molten bath;

(d) transferring at least part of the hot reaction gas from thereduction means to the pre-reduction/melting means as a reducing gas andpartially reducing the metalliferous feed material; and

(e) injecting an oxygen-containing gas into the pre-reduction/meltingmeans and post-combusting a part of the reaction gas and therebygenerating heat which at least partially melts the partially-reducedmetalliferous feed material.

The term “metal rich region” is understood herein to mean the region (orregions) of the molten bath that has a high concentration of metal. Byway of example, the metal layer is one metal rich region.

The term “metal layer” is understood herein to mean that region of thebath that is predominantly metal. Specifically, the term covers a regionor zone that includes a dispersion of molten slag in a metal continuousvolume.

The term “slag layer” is understood herein to mean that region of thebath that is predominantly slag. Specifically, the term covers a regionor zone that includes a dispersion of molten metal in a slag continuousvolume.

The term “transition zone” is understood herein to mean a gas continuousvolume with splashes, droplets, and streams of molten material (which isat least predominantly slag) therein.

One option for generating the upward movement of splashes, droplets andstreams of molten material from the metal layer in step (b) is to injectthe solid carbonaceous material and carrier gas in step (b) via one ormore than one lance/tuyere that extend downwards towards the metallayer.

More preferably the one or more than one lance/tuyere extend throughside walls of the vessel and are angled inwardly and downwardly towardsthe metal layer.

It is preferred that the injection of solid carbonaceous material andcarrier gas into the metal layer be sufficient to generate upwardmovement of splashes, droplets and streams of molten material in afountain-like manner.

The injection of solid carbonaceous material and carrier gas into themetal layer via the downwardly extending lance(s)/tuyere(s) has thefollowing consequences:

(i) the momentum of the solid carbonaceous material/carrier gas causesthe solid carbonaceous material and gas to penetrate the metal layer;

(ii) the solid carbonaceous material, typically coal, is devolatilisedand thereby produces gas in the metal layer;

(iii)carbon predominantly dissolves into the metal and partially remainsas solid;

(iv) the gases transported into the metal layer and generated viadevolatilisation produce significant buoyancy uplift of material fromthe metal layer which results in the above-described upward movement ofsplashes, droplets and streams of material, and these splashes,droplets, and streams entrain further slag as they move through the slaglayer.

The material referred to in paragraph (d) includes molten metal (whichincludes dissolved carbon) and molten slag that is drawn into the metallayer from above the metal layer as a consequence of solid/gasinjection.

Another option, although by no means not the only other option, togenerate the above-described upward movement of splashes, droplets, andstreams of material is to inject solid carbonaceous material and carriergas via one or more than one tuyere in the bottom of the vessel or inside walls of the vessel that contact the metal layer.

Preferably, the pre-reduction/melting means is positioned above thereduction means and communicates with the reduction means so that atleast partially molten, partially reduced metalliferous feed materialdrains downwardly into the reduction means and, more particularly,drains into the vigorously mixed central region of the slag layer in themolten bath. The applicant believes that this leads to more efficientsmelting of the pre-reduced material.

Preferably with this arrangement hot reaction gas generated in thereduction means flows upwardly into the pre-reduction/melting means.

As indicated above, the upward movement of splashes, droplets andstreams of material from the metal layer promotes mixing of materialfrom the metal layer in the slag layer and mixing of material in theslag layer in the metal layer. Preferably, the extent of mixing issufficient so that the slag layer is more or less homogeneous in termsof composition and temperature.

The mixing of material between the layers promotes reduction of metaloxides present in the molten bath by dissolved carbon in metal. In thisconnection the injection of solid carbonaceous material into the metallayer ensures that there are high levels of dissolved carbon (andpossibly solid carbon) in the metal layer and that, as a consequence,the metal layer is strongly reducing.

It is preferred that the level of dissolved carbon in metal be greaterthan 3.5 wt %.

Preferably the process includes the step of preheating the metalliferousfeed material before supplying the metalliferous feed material into thepre-reduction/melting means.

Preferably the process includes discharging reaction gas from thepre-reduction/melting means as an off-gas and preheating themetalliferous feed material with the off-gas, either hot or cold.

Preferably steps (c) and (e) of injecting the oxygen-containing gas intothe vessel and the pre-reduction/melting means post-combust the reactiongas generated in the molten bath to a post-combustion level of at least70%.

The term “post-combustion” means:$\frac{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack}{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack + \lbrack{CO}\rbrack + \left\lbrack H_{2} \right\rbrack}$

where:

[CO₂]=volume % of CO₂ in the reaction gas;

[H₂O]=volume % of H₂O in the reaction gas;

[CO]=volume % of CO in the reaction gas; and

[H₂]volume % of H₂ in the reaction gas.

More particularly, the term “post-combustion” in the context ofpost-combustion in the vessel also means post-combustion in the absenceof any addition of supplementary carbonaceous material for otherpurposes.

Preferably injection of oxygen-containing gas into the vessel in step(c) is via one or more than one lance/tuyere that extend downwardly andinwardly into the vessel and are set back sufficiently to be clear ofmaterial flowing downwardly from the pre-reduction/melting means intothe vessel.

The transition zone is important for three reasons.

Firstly, the ascending and thereafter descending splashes, droplets andstreams of material are an effective means of transferring to the moltenbath the heat generated by post-combustion of reaction gas in thevessel.

Secondly, the material, and particularly the molten slag, in thetransition zone is an effective means of minimising heat loss byradiation via the side walls of the vessel.

Thirdly, dust containing carbon in the transition zone reduces heat lossby radiation to the side walls of the vessel.

Preferably, the vessel includes:

(a) tap holes for discharging molten metal and slag from the vessel; and

(b) one or more than one outlet for transferring reaction gas to thepre-reducing/melting means.

It is preferred that the oxygen-containing gas be oxygen.

According to the present invention there is also provided an apparatusfor carrying out the above-described process.

More particularly the present invention provides an apparatus forproducing metals from a metalliferous feed material which includes: apre-reduction/melting means which partially reduces and at leastpartially melts the metalliferous feed material and a reduction meanswhich completely melts and reduces the at least partially molten andpartially reduced feed material; which reduction means includes a vesselthat contains a molten bath having a metal layer and a slag layer on themetal layer; which pre-reduction/melting means is positioned directlyabove the vessel and communicates with the vessel whereby at leastpartially molten and partially reduced feed material flows downwardlyinto a central region of the vessel; and which reduction means furtherincludes:

(a) one or more than one lance/tuyere which inject solid carbonaceousmaterial with a carrier gas into a metal rich region of the molten bath;

(b) one or more than one lance/tuyere which inject oxygen-containing gasinto the vessel that post-combusts reaction gas generated in the vessel,the one or more than one lance/tuyere extending downwardly and inwardlyinto the vessel and being positioned so as to minimise contact with atleast partially molten and partially reduced feed material flowingdownwardly from the pre-reduction/melting means; and

(c) one or more than one lance/tuyere which inject oxygen-containing gasinto the pre-reduction/melting means that post-combusts at least a partof the reaction gas from the vessel.

The present invention is described further by way of example withreference to the accompanying drawings, of which:

FIG. 1 is a flowsheet, in largely schematic form, of one preferredembodiment of the process and the apparatus of the present invention;and

FIG. 2 is a flowsheet, in largely schematic form, of another preferredembodiment of the process and the apparatus of the present invention.

The following description is in the context of producing molten ironfrom iron ore and it is understood that the present invention is notlimited to this application and is applicable to any suitablemetalliferous material.

With reference to FIG. 1, iron ore is transferred from a series ofstorage bins 3 into a pre-reduction/melting means that is in the form ofa cyclone converter 5 and is partially reduced (by way of example, up toFeO) and at least partially melted in the cyclone converter 5.

The cyclone converter 5 is positioned directly above a reduction meansthat is in the form of:

(a) a metallurgical vessel 7 which contains a molten bath 15 having ametal layer and a slag layer and which has a suitable means (not shown)for tapping molten metal and slag and an outlet for reaction gas thatopens directly into the cyclone converter 5; and

(b) lances/tuyeres 11 for injecting solid carbonaceous material andoptionally fluxes into the vessel 7 and lances/tuyeres 13 for injectingoxygen into the vessel 7, which lances/tuyeres 11, 13 extend downwardlyand inwardly into the vessel through the side wall of the vessel.

A suitable form of the vessel 7 and the lances/tuyeres 11, 13 and asuitable process for reducing metalliferous feed material in the vessel7 is described in general terms in commonly assigned U.S. patentapplication Ser. Nos. 09/535,665 and 09/462,282, the disclosures ofwhich are incorporated by reference.

The process flowsheet of FIG. 1 includes injection of solid material andcarrier gas into the metal layer 15 via the lances/tuyeres 11. Aparticular feature of the preferred process flowsheet is that theinjected solid material is confined to solid carbonaceous material(typically coal) and optionally one or more than one slag forming agent(typically lime). The gases that are generated by and transported intothe metal layer as a consequence of the injection of solid carbonaceousmaterial and carrier gas into the metal layer produce significantbuoyancy uplift of molten metal, solid carbon, and molten slag (drawninto the metal layer as a consequence of solid/gas injection) from themetal layer which generates upward movement of splashes, droplets andstreams of molten material and solid carbon, and these splashes,droplets and streams entrain slag as they move through the slag layer.

The buoyancy uplift of molten material and solid carbon causessubstantial agitation in the metal layer and the slag layer, with theresult that the slag layer expands in volume. The extent of agitation issuch that there is strong mixing of material from the metal layer in theslag layer and strong mixing of material from the slag layer in themetal layer.

In addition, the upward movement of splashes, droplets and streams ofmaterial caused by the buoyancy uplift of molten metal, solid carbon,and molten slag extends into the gas space above the molten material inthe vessel and form a transition zone.

The diameter of the cyclone converter 5 is relatively small compared tothat of the vessel 7 and the cyclone converter 5 is positioned centrallyabove the vessel 7. Accordingly, the at least partially molten,partially-reduced iron ore produced in the cyclone converter 5 flowsdownwardly into the central region of the molten bath 15 and iscompletely reduced in the molten bath 15. The mixing of material betweenthe metal layer and the slag layer ensures that complete reduction isachieved effectively and efficiently.

The reactions that occur in the molten bath 15 in the vessel 7 generatereaction gas (such as CO and H₂) and the gas moves upwardly through thevessel 7. Oxygen produced in an oxygen plant 19 is injected into the gasspace in the vessel 7 above the molten bath 15 via the lances/tuyeres 13and post-combusts a part of the reaction gas in the transition zone andother sections of the gas space. The heat is transferred to theascending and thereafter descending splashes, droplets and streams ofmaterial and the heat is then transferred to the metal layer when themetal/slag returns to the metal layer. In order to avoid damage bycontact with material flowing downwardly from the cyclone converter 5,the lances/tuyeres 5 are set back to be clear of such downwardly flowingmaterial.

The post-combusted reaction gas produced in the vessel 7 flows upwardlyinto the cyclone converter 5 and acts as a reducing gas which partiallyreduces the iron ore supplied to the cyclone converter 5.

In addition, oxygen produced in the oxygen plant 19 is injected into thecyclone converter 5 and post-combusts at least part of the reaction gasin the cyclone converter 5 and generates heat that melts thepartially-reduced iron ore.

The combined level of post-combustion in the vessel 7 and the cycloneconverter 5 is at least 70%.

An off-gas discharges from the cyclone converter 5 via a duct 17. Theduct 17 includes a water cooling assembly 9 which initially cools theoff-gas by means of water panels and thereafter quenches the off-gas andthereby removes entrained solids from the off-gas and reduces the watervapour content of the off-gas.

The quenched off-gas is transferred via a line 27 and is used as a fuelgas or vented flue gas.

The process flowsheet shown in FIG. 2 includes all of the components ofthe flowsheet shown in the figure.

In addition, in the process flowsheet shown in FIG. 2 the iron ore ispreheated in a preheater assembly 29 prior to supplying the iron ore tothe cyclone converter 5. The preheater assembly 29 operates with a partof the fuel gas from the water cooling assembly 9 which is supplied viaa line 31. The use of a preheater assembly 29 is an advantage in termsof productivity and operational costs, particularly in situations wherethe iron ore has high levels of loss of ignition (for example,crystalline water). Moreover, in situations where the iron ore has highlevels of loss of ignition, the preheater assembly 29 has the advantagethat it minimises thermal decrepitation of iron ore particles when theparticles are exposed to high temperatures in the cyclone converter 5.

The Table set out below provides heat and mass balance calculations forthe process flowsheets of FIGS. 1 and 2 under the stated operatingconditions.

Preheater assembly (29) Figure 1 flowsheet Figure 2 flowsheet Fines FeedNot applicable 278 tph @ 25 C Pre-reduction/ melting means (5) FinesFeed 261 tph 266 tph @ 25 C @ 700 C Oxygen 37.1 kNm3/h 28.5 kNm3/hOffgas 252 kNm3/h 222 kNm3/h @ 1800 C @ 1800 C & 77% post combustion &76% post combustion Reduction means (7, 11, 13, 15) Feed rate 221 tph231 tph @ 1600 C @ 1600 C & 22% pre-reduction & 22% Pre-reduction Oxygen71.1 kNm3/h 63.0 kNm3/h Coal 113.0 tph 105.0 tph Flux 7.1 tph 7.8 tphOffgas 226 kNm3/h 208 kNm3/h @ 31.5% post @ 34.9% post combustioncombustion Metal 181 tph 188 tph @ 1500 C @ 1500 C & 4.0% carbon & 4.0%carbon Slag 21 tph 21 tph Offgas from Pre- reduction/melting means (5)Hood cooling 132 MW 118 MW Gas ex Scrubber 211 kNm3/h 88 kNm3/h @ 72%post combustion @ 71% post combustion

The iron ore was sourced from North America and contained 68.2% iron,0.6% SiO₂ and 0.95% Al₂O₃ on a dry basis.

The coal had a heating value of 33.9 MJ/kg, an ash content of 5.4% and avolatiles level of 14%. Other characteristics included 90.0% totalcarbon, 2.0% H₂O, 1.3% N₂, 3.2% O₂ and 4.0% H₂.

Many modifications may be made to the preferred embodiments of theprocess and apparatus of the present invention as described abovewithout departing from the spirit and scope of the present invention.

By way of example, the present invention is not limited to the use ofcyclone converters and extends to any suitable pre-reduction/meltingmeans.

Furthermore, whilst the above described embodiments include injectingall of the solid carbonaceous material into the metal layers in thevessels 7, it can readily be appreciated that the present inventionextends to embodiments in which part of the solid carbonaceous materialis top-charged or otherwise supplied to the vessels 7.

Furthermore, whilst the above described embodiments are confined toinjecting carrier gas and solid carbonaceous material and optionallyslag forming agents into the metal layer via lances/tuyeres 11, it canreadily be appreciated that the present invention extends to embodimentsin which other solid materials, such as metalliferous feed material, areinjected into the metal layers.

What is claimed is:
 1. A process for producing iron-containing metalsfrom a metalliferous feed material which includes the steps of partiallyreducing and at least partially melting the metalliferous feed materialin a pre-reduction/melting means and completely reducing the partiallyreduced feed material in a reduction means, which pre-reduction/meltingmeans is positioned directly above the reduction means and communicateswith the reduction means so that at least partially molten, partiallyreduced feed material flows downwardly into a central region of thereduction means, which reduction means includes a vessel that contains amolten bath having a metal layer and a slag layer on the metal layer,and which process further comprises: (a) injecting solid carbonaceousmaterial and carrier gas into a metal rich region of the molten bath viaone or more than one lance/tuyere that extend downwardly towards themetal layer, the injection of carbonaceous material and carrier gascausing upward movement of splashes, droplets, and streams of materialfrom the metal layer which: (i) promotes mixing of material from themetal layer in the slag layer and mixing of material from the slag layerin the metal layer; and (ii) extends into a space above the molten bathto form a transition zone; (b) injecting an oxygen-containing gas intothe vessel and post-combusting part of a reaction gas generated in themolten bath via one or more than one lance/tuyere extending downwardlyand inwardly into the vessel and being positioned so as to minimisecontact with at least partially molten and partially reduced feedmaterial flowing downwardly from the pre-reduction/melting means; (c)allowing at least part of the reaction gas generated in the molten bathto flow upwardly from the reduction means into the pre-reduction/meltingmeans and partially reduce the metalliferous feed material in thepre-reduction/melting means; and (d) injecting an oxygen-containing gasinto the pre-reduction/melting means and post-combusting a part of thereaction gas and thereby generating heat which at least partially meltsand partially reduces metalliferous feed material and generates the atleast partially molten, partially reduced feed material that flowsdownwardly into the reduction means; and whereby steps (b) and (d)post-combust the reaction gas generated in the molten bath to apost-combustion level of at least 70%.
 2. The process defined in claim 1includes injecting solid carbonaceous material and carrier gas via oneor more than one tuyere in the bottom of the vessel or in side walls ofthe vessel that contact the metal layer.
 3. The process defined in claim1 includes the step of preheating the metalliferous feed material beforesupplying the metalliferous feed material into the pre-reduction/meltingmeans.
 4. The process defined in claim 3 includes discharging reactiongas from the pre-reduction/melting means as an off-gas and preheatingthe metalliferous feed material with the off-gas.
 5. The process definedin claim 1 wherein step (b) includes injecting the oxygen-containing gasinto the vessel via one or more than one lance/tuyere that extenddownwardly and inwardly into the vessel and are set-back sufficiently tobe clear of material flowing downwardly from the pre-reduction/meltingmeans into the vessel.